From 0e732d0997cff08855d98c17af4dd5527f10e419 Mon Sep 17 00:00:00 2001
From: chilaxan <chilaxan@gmail.com>
Date: Mon, 4 Dec 2023 03:15:43 -0500
Subject: [PATCH] gh-112625: Protect bytearray from being freed by misbehaving
 iterator inside bytearray.join (GH-112626)

---
 Lib/test/test_builtin.py                        | 17 +++++++++++++++++
 ...23-12-03-19-34-51.gh-issue-112625.QWTlwS.rst |  1 +
 Objects/bytearrayobject.c                       |  5 ++++-
 3 files changed, 22 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Core and Builtins/2023-12-03-19-34-51.gh-issue-112625.QWTlwS.rst

diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
index b7966f8f038..535856adaea 100644
--- a/Lib/test/test_builtin.py
+++ b/Lib/test/test_builtin.py
@@ -2039,6 +2039,23 @@ class BuiltinTest(unittest.TestCase):
         bad_iter = map(int, "X")
         self.assertRaises(ValueError, array.extend, bad_iter)
 
+    def test_bytearray_join_with_misbehaving_iterator(self):
+        # Issue #112625
+        array = bytearray(b',')
+        def iterator():
+            array.clear()
+            yield b'A'
+            yield b'B'
+        self.assertRaises(BufferError, array.join, iterator())
+
+    def test_bytearray_join_with_custom_iterator(self):
+        # Issue #112625
+        array = bytearray(b',')
+        def iterator():
+            yield b'A'
+            yield b'B'
+        self.assertEqual(bytearray(b'A,B'), array.join(iterator()))
+
     def test_construct_singletons(self):
         for const in None, Ellipsis, NotImplemented:
             tp = type(const)
diff --git a/Misc/NEWS.d/next/Core and Builtins/2023-12-03-19-34-51.gh-issue-112625.QWTlwS.rst b/Misc/NEWS.d/next/Core and Builtins/2023-12-03-19-34-51.gh-issue-112625.QWTlwS.rst
new file mode 100644
index 00000000000..4970e10f3f4
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2023-12-03-19-34-51.gh-issue-112625.QWTlwS.rst	
@@ -0,0 +1 @@
+Fixes a bug where a bytearray object could be cleared while iterating over an argument in the ``bytearray.join()`` method that could result in reading memory after it was freed.
diff --git a/Objects/bytearrayobject.c b/Objects/bytearrayobject.c
index 67073190cc8..659de7d3dd5 100644
--- a/Objects/bytearrayobject.c
+++ b/Objects/bytearrayobject.c
@@ -2007,7 +2007,10 @@ static PyObject *
 bytearray_join(PyByteArrayObject *self, PyObject *iterable_of_bytes)
 /*[clinic end generated code: output=a8516370bf68ae08 input=aba6b1f9b30fcb8e]*/
 {
-    return stringlib_bytes_join((PyObject*)self, iterable_of_bytes);
+    self->ob_exports++; // this protects `self` from being cleared/resized if `iterable_of_bytes` is a custom iterator
+    PyObject* ret = stringlib_bytes_join((PyObject*)self, iterable_of_bytes);
+    self->ob_exports--; // unexport `self`
+    return ret;
 }
 
 /*[clinic input]